In medical engineering, especially in surgery, in particular surgical interventions bone screws are set, for example so-called pedicle screws which are used in spinal surgery. For this purpose, at first a drilling operation has to be carried out so that then a screw can be set into each hole drilled into the vertebra body. Unfortunately, all bones/vertebrae to be treated have a different brittleness. Therefore, a certain sensitiveness is required to accurately set the bore and to introduce the screw in a non-destructive manner/i.e. without damaging the vertebra body. However, especially critical are the last phase of the drilling operation and the last phase of the screwing operation. Until then, a lot of rotational movements are required to create the borehole and to introduce the screw sufficiently deeply so that the risk of tear-out of the vertebra bone or over-tightening of the screw will increase especially in the respective final phase of the drilling and screwing operation.
Manual screwing-in of surgical screws results in rapid fatigue of the surgeon's hand and arm muscles due to the repetitive movement, however. This may result in a negative operation outcome and also may cause long-term symptoms among physicians.
Therefore, it has always been desirable to make use of a motor drive unit (electric, hydraulic or pneumatic motor) so as to provide a torque. In so doing, frequently electric motor drive units, i.e. drive motors comprising an electric motor, are used which are either supplied with power depending on a battery/an accumulator or else make use of an external power supply via a cable.
There are known already so-called transfixion wire chucks constituting attachments for surgical drills which make use of a lever for fulfilling a specific function. A transfixion wire is guided through the machine. When the lever is pulled, the wire is clamped in the motor so that it can be made to rotate by the drive unit. In this way, the wire can be turned into a tissue. Upon release of the lever, the wire can be moved in an axially and rotationally free manner in the motor. This principle is further pursued also in other medical devices.
From the state of the art, for example an electric cable-bound screwing pistol is known from U.S. Pat. No. 8,786,233 B2, which belongs to the same family as EP 2 701 879 A1. There an electric ratchet for a driven screwdriver is disclosed. Said known ratchet is designed so that, unless a trigger is actuated, the electronic ratchet is activated. The user may choose at an additional operating unit between clockwise and anti-clockwise rotation as well as blocking into both directions.
The ratchet is electrically configured/activatable resulting in the fact that for ensuring the ratchet to block such high current flows in the motor that a strong heat development will occur. In addition, acoustic feedback is missing. In this case, manual ratcheting carried out for drilling in the final drilling phase, for example, or mechanical ratcheting used during thread-cutting, as it is also used in the last phase of screwing, for example, is not provided. As the system is cable-bound, also the reach/freedom of movement is strongly limited. Furthermore, it is a drawback of this system that a closed system is presented and inadvertent actuation of the trigger during manual screwing results in a sudden penetration of the screw or in a sudden continued drilling. This is disastrous when applied to a patient, however.
Screw attachments are also known from other manufacturers, for example the Surgical Drill Set 510.01 manufactured by Synthesis. An attachment which reduces the output speed of the drill pistol to about 300 Rpm can be attached to said drill pistol. For use, it is additionally prescribed to attach a torque limiter to this screw attachment. It is a drawback that such torque limiters are not adjustable and are easily available only at predefined values of 0.4 Nm, 0.8 Nm, 1.5 Nm and 4 Nm. Furthermore, this system cannot be used for manual screwing and tightening of screws. Therefore, a tool change is always required. In practice, also the torque limitation turns out to lack flexibility. Manual screwing-in of a screw by a mechanical ratchet, for example by means of a screwdriver having an integrated ratchet, is not useful, either, although it is advantageous in this case that changing the grip during the screwing operation is avoided. It is a drawback that, despite the use of a ratchet, such repetitive movement resulting in fatigue of the muscles is still required and thus may also directly negatively affect the outcome of operation. The symptoms of the physicians are not avoided, either.
It is another drawback of the various systems that they can be employed either for plate screw joints only or for polyaxial screws only. Polyaxial screws in this context are e.g. screws having a spherical screw head which is enclosed by a case so that the case is freely adjustable relative to the longitudinal axis of the screw. In particular pedicle screws are configured in this way.